1. The Field of the Invention
The present invention relates to fluoride containing glass compositions that may be used not only to help prevent demineralization of teeth, but also to alleviate pain and/or sensitivity of a patient's teeth.
2. The Relevant Technology
Dental caries consist of demineralization of a tooth caused by bacteria. In the early stages of caries a white spot develops on the tooth and if the disease is not halted and reversed, the enamel surface breaks down to form a lesion. This can then lead to decay and eventually, a fractured tooth. It is well known that development of dental caries may be reduced by means of various factors, such as diet and oral hygiene measures, anti-microbial treatments and the provision of fluoride to the teeth.
Tooth sensitivity is also a common problem affecting children and adults. Generally, tooth sensitivity may be caused by gingival recession, dentine exposure due to erosion or abrasion, or periodontal surgery that includes root planning. Such conditions leave the dentinal tubules of the tissue susceptible to irritation by chemical, bacterial, mechanical or thermal stimuli. Examples of stimuli include heat, cold, and sweet foods. It is believed that tooth sensitivity is the result of nerve endings of the dental pulp being excited by fluid flow through the exposed dentinal tubules.
Treatments directed to alleviating pain associated with sensitive teeth have generally focused on blocking access to the dentinal tubules so as to prevent stimuli from causing pain and sensitivity. Many treatments have been developed which include application of inorganic or organic components designed to plug or otherwise block dentinal tubules for a limited time. A disadvantage of such treatments is that normal habits such as eating certain foods (e.g. foods with a high acid content) or brushing can negate the treatment. Recently, testing has revealed that increased fluoride levels within the mouth may also be used as a treatment for tooth sensitivity (Toumba and Andreadis).
Current methods for administering fluoride for caries prevention include the fluoridation of drinking water, the ingestion of fluoride tablets, the incorporation of fluoride into mouth washes, toothpastes, and foods, the topical application of fluoride solutions, gels and varnishes and recently, the incorporation of fluoride in dental materials and devices.
Evidence supports the concept of frequent applications of relatively low concentrations of fluoride ions for the prevention of caries and the treatment of sensitive teeth. A sustained and controlled release delivery system could help to achieve this goal.
Although glass compositions that release fluoride ions in the mouth have proven useful for caries prevention, they have also exhibited various difficulties. Silicate glasses from which fluoride can be slowly leached have been disclosed in U.S. Pat. No. 4,920,082 and WO 88105652, but these glasses generally exhibit low fluoride retention, while requiring high batch melting temperatures. The use of phosphate as a glass former has been known for many years. However, the disadvantage of these glasses is that they are easily attacked by water. This property has been exploited for the development of soluble glasses for use in animal health releasing copper, cobalt, and selenium to ruminant animals over 6 to 12 months as the glass dissolves (GB Pat. No. 2116424). A more slowly dissolving glass has been used to provide copper ions in an anti-fouling paint for use on ships. This glass was formulated to dissolve over 5 years (EP App. No. 94906287.1).
Hence, existing glass compositions have not been entirely satisfactory for use in slow fluoride release intra-oral devices. The low retention of many fluoride containing glasses means that the release of fluoride is not maintained over a sufficiently long period of time. In addition, the low retention would require a relatively large piece of glass to be fixed to the tooth of the patient to provide sufficient levels of fluoride release into the mouth. This would be obtrusive and reduce the appeal of the device to a patient.